iowa is where barack obama's drive for the presidency got its start. >> and you welcomed me and michelle into your homes. >> reporter: and then it happened. >> and mr. obama got teary-eyed. >> wiped a tear from his face. >> an emotional night, even for a president known for keeping his cool. >> reporter: maybe it was the cold making him cry. nah. >> to say one thing to all the young people. >> reporter: not once, but three times -- >> to all of you who have lived and breathed the hard work of change, i want to thank you. >> reporter: the president used his finger -- >> who believe we've got all something to contribute. >> reporter: -- to dab away a tear. no surprise the president's had some of his critics crying. crying foul. who cries from just one eye, asks someone calling herself joanie baloney. the president has cried before at a funeral for a civil rights activist as michelle eyed his watering eyes. and four years ago, exactly one day before the election -- >> it's hard to talk about. >> reporter: then senator obama lost the grandmother who helped raised him and this time thumbed aw